I've thought about this a lot in relation to Catholic teaching as it's one of the fundamental reasons (along with attitudes to homosexuality) that I can't fully embrace the Catholic faith I was baptised into. There's a lot of good in Catholicism and I'm really attracted to being part of a faith-based community, but I can't get past the attitude to abortion.
One of the teachings that I do agree with is that we cannot know the point at which the foetus becomes a human. Most of you won't believe that this is determined by God, but it is one of those questions that science can't really answer. When we think of our own children, we can all think of aspects of their personality that were unique and special to them from their first day of life, but at what point did these originate. The day they were conceived? Week 12? Week 24? It's from this belief that the Catholic teaching on abortion proceeds - we can't know the point at which this embryo becomes a human life, so we can't know if we are taking a human life if we abort it.
Catholic teaching on sex and relationships is therefore - at least - consistent. That sexual intercourse should take place only within marriage (the implication is that it is therefore consensual, which is not necessarily true, as we know) so that - in theory - any life which is procreated as a result can be loved, cherished and welcomed into the world. Hardline Catholics fondly imagine that if everyone followed Catholic teaching and only had sex within marriage, then there would be no need for contraception or abortion.
In real life of course, this doesn't happen. What I particularly hate about pro-life campaigners (especially the men) is the way they focus on the behaviour of women, as though they were the sole cause of abortion occurring (because - duh! - no man has ever had an abortion.....). I'm happy to be contradicted but I believe that non-consensual sex is a big driver of abortion rates, and I believe that it's the behaviour of men that is the biggest cause of this.
Earlier posters said that they wanted to see more sex education and for GIRLS to be taught self-respect. Hateful Nadine Dorries says that she wants to see lessons in abstinence for girls only. What good will that do them if a man decides he wants to have sex with one of them and won't take no for an answer?
If we want to reduce the rates of abortion (and I do, while firmly supporting a woman's right to have one, regardless of my Catholic faith), then we need to focus on men's behaviour and wider cultural attitudes towards sex. Something that I actually believe the churches could do a lot to influence, if they wanted to.